Intra-aortic balloon pumps (IABP) are used to provide counter pulsation within the aorta of ailing hearts over substantial periods of time, e.g. to provide ventricular assistance during cardiogenic shock, low cardiac output in post-operative care, weaning from cardiopulmonary bypass, treatment for refractory unstable angina, and other circumstances of subnormal cardiac function. Such pumps of the type involved in this invention include a flexible intra-aortic balloon (IAB) which is readily inflatable under low pressure to substantial size and displacement. The balloon is mounted on a catheter device used for insertion of the balloon into a remote artery, typically a femoral artery, and through the intervening vascular system of the patient to the aortic pumping site while the balloon is deflated and furled. This requires insertion of the furled large capacity balloon through a small insertion passage, e.g., a small puncture opening or through an introducer cannula into the selected artery, and then sliding-threading of the catheter and furled balloon through tortuous lumen passageways of the patient's vascular system over a guidewire to the pumping site, e.g. from insertion into an artery in the groin area to the patient's descending aorta. At the pumping site, the balloon is unfurled and then successively and rapidly inflated and deflated in synchronism with the patient's cardiac pulsation rates over extended periods of time in a known counterpulsation technique to enhance cardiac output. Thus, use of an IABP requires forceful sliding insertion of a relatively large balloon through a small insertion opening and tortuous arterial lumens, which may be randomly narrowed by arteriosclerotic deposits of plaque, and subsequent unfurling and reliable pulsation operation at heartbeat rates over substantial periods of time, e.g. for several days.
It will be appreciated that the circumstances and requirements of insertion and use of intra-aortic balloon pumps provide numerous conflicting parameters. Significant aspects of these conflicting parameters are related to the fact that the inflated but unstretched diameter of the balloon is much larger than the diameter of the insertion site, which may be percutaneous, and larger than at least portions of the lumen of the vascular system through which it is to be threaded. This requires that the balloons be furled for insertion through passageways which are of very small inside diameter (ID) relative to the size of the balloon when opened. The related catheter equipment typically must include dual concentric lumens, including an inner lumen passageway to serve functions such as engaging over a guidewire, sensing values in the aorta, e.g. arterial pressure, and/or administration of medicaments. A surrounding annular passageway between the inner and outer lumens must be of a size adequate to shuttle an operating gas such as helium at rates to obtain the rapid repetitious expansion and collapse of the balloon necessary for the pumping function in counterpulsation to the patient's heart.
The aforenoted parameters for intra-aortic balloon catheters have resulted in these catheters being of significant complexity of construction and attendant substantial size, i.e. substantial effective diameter of the catheter structure during insertion as well as during the periods of pumping operation within the patient's vasculature. A significant potential complication during use is associated with limb ischemia due to size mismatch between the overall size (diameter) of the counter pulsation catheter and the effective lumen size of the patient's vasculature through which the catheter must pass and in which it must remain during the period of pumping assistance. Heretofore, the full featured IAB catheter systems available on the market have been of nominal 9 French (Fr) size or larger. The Fr size designation of an IABC refers to the approximate size of the outer lumen. Thus, for example, while 9 Fr literally is about 0.118" diameter, catheters designated as 9 Fr may have outer lumens which slightly exceed that dimension, e.g., up to about 0.122". Further, such catheters may include balloons which originally were furled to about 0.126" outer diameter and in which the furling has relaxed to about 0.144" outer diameter in their packaging sheaths. In any event, reduction in size of intra-aortic balloon catheters and introducer systems would improve systemic flow to limbs at risk.
However, as indicated above the insertion of an IAB catheter intrinsically involves pushing the device along a tortuous path through the patient's vasculature. This requires applying and transmitting compressive forces through the very slender "column" structure of the catheter, which requires a significant degree of stiffness in the catheter. The catheter also must flex or bend to follow the desired path through the patient's vasculature without undue lateral reactive force which could cause trauma to the vessels. Thus IAB catheters should have a high degree of stiffness over a wide range of bending angles, while providing flexibility to follow tortuous paths along which the IAB catheter is being pushed. These characteristics are measures of the "pushability" and "trackability" of the catheter, e.g., to follow a guide wire when pushed therealong over a tortuous path without overcoming the guiding stiffness of that wire and/or otherwise impinging on the vasculature walls with potentially injurious forces.
IAB catheters also must resist kinking, i.e., sharp bending collapse of either or both of the lumen tubes with attendant loss of smooth curvature and closing or drastic reduction of the respective internal passageway. Resistance to kinking is necessary to maintain pushability of the catheter assembly and to avoid binding on the guide wire. Avoiding kinking also minimizes risks of cracking of the lumens during insertion and attendant risks of later leakage during operation, as well as minimizing risks of kink-blockage of the gas shuttle capacity between the lumens or blockage of medication or sensing operations through the inner lumen during pumping operation.
It is an object of this invention to provide improved intra-aortic balloon pump catheters.
It is a more specific object of this invention to provide such catheters wherein adequate gas shuttling capacity can be obtained with conventional pump controllers through catheters of significantly reduced size.
Similarly, it is an object of this invention to provide such improved catheters wherein substantially higher gas flow rates and attendant higher shuttle speeds may be obtained in catheters of sizes used heretofore, thereby permitting tracking of heart rhythms not trackable with conventional previous catheters.
It is a further object to provide improved IAB catheters which attain some or all of the aforegoing objects and which maintain high degrees of flexibility, torquability, pushability and trackability for safe and easy insertion, with minimal risk of trauma to the patient.